The present invention relates to an apparatus for sensing a characteristic of a traveling yarn, and more particularly to such an apparatus acting in response to the shadow cast by the yarn or its reflection on a light sensing element as the yarn travels through a slot of an apparatus supporting the light sensing element and a light emitting source.
Apparatus for sensing characteristics of traveling yarn are known and one type of apparatus includes a light emitting source spaced from a light sensing element and adapted to monitor changes in the light sensed by the light sensing element as a yarn travels within the space between the light sensing element and the light emitting source. However, problems arise in the operation of these types of yarn sensing apparatus due to, among other reasons, the accumulation of dust, dirt or the like on the light emitting or light sensing elements and the presence of light emitted from sources other than the light emitting source. Both these operational problems distort the accuracy of the sensing based upon the light sensed by the light sensing member.